Semiconductor devices, for example, transistors, light emitters and detectors, fabricated using III-V semiconductor materials, have become scientifically and commercially important because of properties such as high speed, low loss, low noise operation, and relatively efficient generation and detection of light. For example, III-V light-emitting diodes and laser diodes are sold commercially for various applications.
So-called catastrophic optical damage (COD) and power saturation resulting from junction heating have long limited the maximum output powers available from semiconductor lasers [see C. H. Henry et al., J. Appl. Phys. 50, 3721 (1979)]. To alleviate these effects, a variety of different "window" lasers with higher COD levels have been successfully fabricated. The windows can serve to prevent damaging current levels at or near the laser facets (cleaves). These include non-absorbing windows formed by both Zn and Si impurity induced layer disordering (IILD) [see Y. Suzuki et al., Electron. Lett. 20, 383 (1984); R. L. Thornton et al., Appl. Phys. Lett. 49, 1572 (1986); W. D. Laidig et al., Appl. Phys. Lett. 38, 776 (1981); and D. G. Deppe and N. Holonyak, Jr., J. Appl. Phys. 64, R93 (1988)], or by etching and crystal regrowth [see J. Unger et al. Electron. Lett. 22, 279 (1986)]. Zn disordered windows typically suffer from significant free carrier absorption in the active layer. Windows formed by Si IILD or by etching and crystal regrowth are limited more by scattering losses near the window transition region, resulting in increased laser thresholds and decreased efficiencies. Smaller improvements in the COD level have also been demonstrated with absorbing current blocking windows [see T. Shibutani et al., J. Quantum Electron. QE-23, 760 (1987)]. In all of the above cases, the window regions are defined by planar or non-planar processing (of varying complexity), followed by cleaving of laser bars near the center of the window regions. This necessarily results in windows of varying length that are large enough to cleave easily.
It is among the objects of the present invention to improve fabrication of III-V semiconductor light emitting devices and other devices to facilitate their fabrication, and to obtain devices having improved operating characteristics and improved reliability and life.
In the fabrication of III-V semiconductor devices, it is typical to deposit layers on a substrate to form a structure of relatively large surface area (sometimes called a "crystal") that is processed and is separated, such as by cleaving and/or sawing and/or etching, into many individual devices, or groups of devices, of relatively small area. [These may sometimes remain on a common base.] Applicant has found that the separating of the crystal, and/or other processing operations, can result in microscopic cracks and other structural defects that have a deleterious effect on ultimate operation of the devices being fabricated.
It is also among the objects of the present invention to improve fabrication of III-V semiconductor devices to minimize the effects of structural defects.